MONDAY, June 9, 2014 (HealthDay News) -- Men who carry a cellphone in their pants pocket may harm their sperm and reduce their chances of having children, a new review warns.

The research team analyzed the findings of 10 studies that examined how cellphone exposure may affect male fertility. Among men with no exposure to cellphones, 50 percent to 85 percent of their sperm had a normal ability to move towards an egg.

That fell by an average of 8 percent among men exposed to cellphones. Similar effects were seen for sperm viability, which refers to the proportion of sperm that were alive, according to the study published June 9 in the journal Environment International.

The effects of cellphone exposure on sperm concentration (the number of sperm per unit of semen) were unclear, the investigators noted.

Most adults worldwide own mobile phones, and about 14 percent of couples in middle- and high-income nations have difficulty conceiving, the researchers said. They also noted that previous studies have suggested radio-frequency electromagnetic radiation emitted by cellphones can harm male fertility.

"Given the enormous scale of mobile phone use around the world, the potential role of this environmental exposure needs to be clarified," study leader Fiona Mathews, of the biosciences department at the University of Exeter in England, said in a university news release.

"This study strongly suggests that being exposed to radio-frequency electromagnetic radiation from carrying mobiles in trouser pockets negatively affects sperm quality. This could be particularly important for men already on the borderline of infertility, and further research is required to determine the full clinical implications for the general population," she said.

While the study found an association between cellphone exposure and male infertility, the study was not designed to determine a cause-and-effect relationship.